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BASIC OF PHYTOPATHOLOGY
2. LECTURE
CAUSES AND AGENTS OF
PLANT DISEASES AND DISORDERS
© 2012 A. Lebeda, B. Mieslerová, M. Sedlářová
CAUSES AND AGENTS OF
PLANT DISEASES AND DISORDERS
I.
Abionosis -Non-infectious causes or physiological disorders
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Extreme temperatures
Extreme soil wetness
Excess or lack of light
Oxygen deficiency
Air pollution, exposure to emissions
Nutrient deficiency (macroelements (K,Ca), microelements (B))
Inappropriate pH
Inappropriate agrotechnic management
The toxicity of pesticides
Toxicity of minerals
CAUSES AND AGENTS OF
PLANT DISEASES AND DISORDERS
II. Infections (biotic) disease (and damage)
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Viruses and viroids
Prokaryots (Bacteria and Phytoplasmas)
Fungi
Parasitic higher plants and green algae
Protozoa
Nematodes, mites, insects
EXAMPLES OF ABIOTIC DISORDERS
EXAMPLES OF ABIOTIC DISORDERS
Frost damage of cherries (Prunus)
Drought in Spruce (Picea)
Ozone damage on Nicotiana tabacum
INFECTIOUS AGENTS OF DISEASES
 Bionosis – infectious diseases
 A. NON-CELLULAR ORGANISMS
A.1. Viroids
A.2. Viruses
 B. PROKARYOTIC ORGANISMS
B.1. Bacteria
B.2. Phytoplasmas
 C. EUKARYOTIC ORGANISMS
C.1. Fungi
C.2. Algae
C.3. Higher plants
C.4. Protozoa
C.5. Nematodes, mites, insects
MORPHOLOGY AND WAYS OF MULTIPLICATION OF SOME OF THE GROUPS
OF PLANT PATHOGENS
SCHEMATIC DIAGRAM OF
THE VARIOUS PLANT
PATHOGENS IN HOST
CELL
A. NON CELLULAR ORGANISMS
A.1. Viroids
 Uncoated, small, circular, single-stranded RNA, which replicated
autonomously when inoculated into a host plant.
 They differ from viruses or bacteriophages by absence of a protein
capsid and a small genom.
 The smallest known agents of infectious plant diseases.
Discovered to r. 1971, until most of the diseases caused by viroids
were considered to be viral diseases.
 It is not known how viroids actually replicate probably all
components necessary for their replication provides host.
 Pathogenesis modifies metabolic regulatory networks, the
transcription of a number of genes, transcription factors and their
ability to activate promoters
A. NON CELLULAR ORGANISMS
A.1. Viroids
 Most of viroids is localized in the nucleus of the host cell, usually
they are transmitted by sap (míza) also by pollen or vegetatively.
 They are resistant to high temperatures.
 Most of viroids causes in the infected plants no symptoms.
General symptom of infected plants are dwarf growth, epinastic
deformation and creased leaves.
 To date, it was found that around 40 different plant diseases are
caused by viroids. Viroids act only disease in plants. They were not
found in animals and humans.
Taxonomy of viroids
Avsunviroid (ASBVd)-replication occurs in chloroplasts
Pospiviroid (PSTVd)- replication occurs in nucleus
Unassigned viroides
SYMPTOMS CAUSED BY VIROIDS
Potato spindle tuber disease
Chrysanthemum
stunt disease
Examples of diseases caused by
viroids
POTATO SPINDLE TUBER - Potato
spindle tuber viroid (PSTVd)– It causes
big losses, attacks all varieties and is
spreading rapidly
CITRUS
EXOCORTIS
(Citrus
exocortis
viroid)
CACANGCADANG of
COCONUT PALM
(Coconut cadangcadang CCCVd) –
On Phillipines
devastates coconut
palms
CHRYSANTHEMUM
STUNT
(Chrysanthemum stunt
viroid – CSVd)
A. NON CELLULAR ORGANISMS
B. A. 2. Viruses
 Obligate parasites reproducing only in host cells (replication is
dependent on the host cell). They usually have a very narrow host
range.
 They attack all species of living organisms, distinguish plant
viruses, animal viruses and bacteriophages (viruses on bacteria).
Recently it is described about 2000 species of viruses, half of them
infecting the plant.
 Diseases caused secondly disturbance of metabolism in the cells
and the use of energy in cells.
STRUCTURE OF VIRAL PARTICLES
• Virion - virus particles,
which is composed of
protein and one type of
nucleic acid (ss RNA, ds
RNA, ss DNA, ds DNA)
• Protein component capsid not only protects
the nucleic acid, but
generally increases the
infectivity of the virus
ELECTRON
MICROPHOTOGRAPHS OF
DIFFERENT MORPHOLOGICAL
TYPES OF VIRUSES
A. NON CELLULAR ORGANISMS
B. A. 2. Viruses
 TRANSFER - viruses get into cells mostly through injuries or
transmission of sucking insects, nematodes, by fungal vectors
(Polymyxa, Spongospora, Olpidium), seeds, pollen, vegetative
propagation. In the plant virus spreads by plasmadesm and then
by the vascular bundles.
 SATELIT VIRUSES They represent the highest level of parasitism.
These are virus particles, which can not occur separately, but only
with a different virus particles - in the tobacco mosaic virus
(Tobacco necrosis satelite virus). Their replication is dependent on
the synthesis of viral RNA.
 PROTECTION AGAINST VIRUSES - quarantine: control of vectors insects, using clear seeds, virus inactivation by heat. It is not yet
known chemical control.
PLANT VIRUS TRANSMISSION
PLANT VIRUS TRANSMISSION
II.
INSECT VECTORS OF PLANT VIRUSES
TRANSMISSION OF PLANT VIRUSES BY NEMATODES, MITES AND
FUNGI
SYMPTOMS OF VIRUSES ON
PLANTS
VIRAL PLANT – growth retardation,
dwarfism, shortened internodes, wilting
FLOWERS - the colorfulness of
the flowers, streaking
LEAVES – chlorotic or
necrotic lesions, mosaic, vein
yellowing, stripes,
deformaiton
Histological
symptoms –
hyperplasy,
hypoplasy,
necrosis
Cytological
changes –
formation of
incluses
SYMPTOMS OF VIRUSES ON PLANTS
SYMPTOMS OF VIRUSES ON PLANTS
CURRENT PLANT VIRUSES TAXONOMY
I: Single-stranded (+)sense DNA (+ ssDNA) single stranded DNA
II: Double-stranded DNA with RNA intermediate (ds DNA (RT) (double
stranded DNA, replicates using reverse transcriptase)
III: Single-stranded (+)sense RNA (+ ssRNA) single stranded RNA
(replicate using polymerase; RNA with function m-RNA)
IV: Single-stranded (-)sense RNA (-ssRNA) single RNA complementary
to m-RNA
V: Single-stranded (+)sense RNA with DNA intermediate in life-cycle
(ssRNA (RT)) single stranded RNA (replicates using reverse transcriptase)
VI: Double-stranded RNA (dsRNA) double stranded RNA
REPRESENTATIVE EXAMPLES OF INDIVIDUAL GROUPS OF VIRUSES
I. ssDNA – single stranded DNA Geminiviridae – Maize streak virus (MSV)
On maize (Zea mays)
II. (ds DNA (RT) double stranded
DNA, replicates using reverse
transcriptase
Cauliflower mosaic virus (CaMV) –
on cauliflower (Brassica oleracea
var. botrytis)
III. (+) sense ssRNA viruses (single stranded RNA (replicate using
polymerase; RNA with function m-RNA)
Bromoviridae, Caliciviridae, Comoviridae, Coronaviridae (Pea enation
mosaic virus), Potyviridae (Potato virus Y), Flaviviridae, Leviviridae
(Tobacco necrosis virus, Barley yellow dwarf virus), Sequiviridae,
Tetraviridae (Tobacco mosaic virus), Tombusviridae
Pea enation
mosaic virus
(PEMV) – on pea
(Pisum sativum)
Barley yellow dwarf
luteovirus (BYDV)
on barley (Hordeum
vulgare)
Tobacco mosaic virus (TMV)
on tobacco (Nicotiana
tabacum)
IV. (-) sense ssRNA viruses – single RNA complementary to m-RNA
Rhabdoviridae (Lettuce necrotic yellows virus), Bunyaviridae,
Orthomyxoviridae.
Lettuce necrotic
yellows virus (LNYV)
- on lettuce (Lactuca
sativa)
V. ssRNA (RT) single stranded RNA (replicates using reverse transcriptase)
Pseudoviridae
VI. ds-RNA – double stranded RNA Reoviridae
Rice ragged stunt virus (RRSV)
on rice (Oryza sativa)
B. PROKARYOTIC ORGANISMS
ONLY REPRESENTATIVES OF GROUP BACTERIA CAUSE PLANT DISEASES
B. TAXONOMY of BACTERIA
BACTERIA
AS PLANT PATHOGENS
GRACILICUTES (GRAM-NEGATIVE BACTERIA)
CLASS: PROTEOBACTERIA
(families Enterobacteriaceae (Erwinia), Pseudomonadaceae
(Pseudomonas, Xanthomonas), Rhizobiaceae (Agrobacterium)
FIRMICUTES (GRAM-POSITIVE BACTERIA)
CLASS ACTINOBACTERIA
Streptomyces, Clavibacter
CLASS FIRMICUTES
(Bacillus, Clostridium)
MOLLICUTES (Spiroplasma, Phytoplasma)
BACTERIAL TAXONOMY
• Bacterial /Archaeal species are defined on the basis of phenotypic
and genotypic differences.
• A bacterial strain is a population of organisms that descends from
a single organisms or pure culture
• A bacterial species is a collection of strains that share main stable
characteristics and differ significantly from other groups of strains
BIOVARS – differ biochemically or physiologically
MORPHOVARS – differ morphologically
SEROVARS – differ in antigenic properties
B.1. BACTERIA
 Prokaryotic organisms, their DNA is not coated by nuclear membrane.
Do not contain membrane organelles (mitochondria, nucleus, plastids
..)
 They have cell walls (one exception representatives of - Mollicutes).
 They have tremendous ability of propagation (usually division, and
budding)
 They occur mainly in warm and moist areas
 Expansion of bacteria - water, insects, animals, humans
 MORPHOLOGY OF BACTERIA - bacteria can be
rod-shaped, oval, spiral, fibrous, with flagella or
without flagella, they can produce spores or not.
Protein capsid. Nucleoid - a circle of DNA;
plasmids.
DETERMINATION OF BACTERIA : shape, number
and location of flagella, Gram stain, infestation
symptoms (wilting, spotting), cultivation - shape,
coloration of colonies, biochemical tests,
serology, molecular identification methods –
RFLP, PCR.
MORPHOLOGY OF BACTERIA
Rod-shaped (A), oval
(B,C,D), spiral (E), fibrous
(G)
G
Monotricha
Number of flagella: monotrichous (1),
polytrichous (more than 1)
The arrangement of flagella:
monopolar, bipolar, lofotrich, peritrich,
amfitrichal, atricha
Monopolar
Peritrich
Polytricha
Lofotrich
Amfitrich
(bipolar
lofotricha)
MEANS OF DISSEMINATION OF BACTERIA (AND FUNGI)
SYMPTOMS OF BACTERIA
INFECTION ON PLANTS
Discoloration
Anthracnosis, necrosis
Clavibacter michiganense
wallnut
Xanthomonas campestris
Bacterial wilting - break down
the walls of the xylem
Pseudomonas syringae pv.
lachrymans
Erwinia tracheiphilla
SYMPTOMS OF BACTERIA INFECTION ON PLANTS II.
Bacterial soft rot
Bacterial canker
Erwinia carotovora subsp.
Carotovora /Pectobacterium/
Formation of tumors
Pseudomonas syringae
pv. syringae
Agrobacterium tumefaciens
SYMPTOMS OF BACTERIA INFECTION ON PLANTS III.
Bacterial common scab
Soil bacteria on the roots of
legume plants
Capable of fixing of
atmospheric nitrogen
Streptomyces scabies
Rhizobium sp.
SIMPLE SCHEME FOR THE DIFFERENTIATION OF GROUPS OF
PHYTOPATHOGENIC BACTERIA
THE MOST IMPROTANT GENERA OF BACTERIAL PLANT PATHOGENS
GRAM NEGATIVE (PROTEOBACTERIA)
Agrobacterium – is closely related to the genus Rhizobium, it causes
tumors by genetically modifying host cells to tumor cells
Erwinia/Pectobacterium – mobile, pectolytic enzymes, infects only
plants
Pseudomonas – causing spotting and cancer, have a wide host
range and also live on the surface of epiphytic plants
Ralstonia – previously referred to the genus Pseudomonas – but it
differs in that it does not produce fluorescent enzymes
Xanthomonas – have a high host specificity and cause wilting and
leaf blotch
Xylella - aerobic, unicellular and producing long chains under
certain conditions, requires special media, because normally
inhabits the xylem.
GRAM POSITIVE (FIRMICUTES)
Clavibacter (Corynebacterium) - mostly immobile
Streptomyces - form mycelium (chains cells), produce antimicrobial
substances against fungi, bacteria, algae, viruses, protozoa and
tumor tissues
GRAM NEGATIVE BACTERIA (PROTEOBACTERIA)
Agrobacterium
Erwinia
/Pectobacterium/
carotovora
Erwinia amylovora
GRAM NEGATIVE BACTERIA (PROTEOBACTERIA)
Pseudomonas
Pseudomonas
syringae var.
syringae
Ralstonia
solanacearum
GRAM NEGATIVE BACTERIA (PROTEOBACTERIA)
Xanthomonas
Xanthomonas campestris
pv. campestris
Xylella fastidiosa
GRAM – POSITIVE BACTERIA (FIRMICUTES)
Clavibacter michiganensis
Streptomyces scabies
THE MOST IMPORTANT GENERA OF PLANT PATHOGENIC BACTERIA
B. PROKARYOTIC ORGANISMS
B.2. MOLLICUTES
 MOLLICUTES –
 They are referred to the group Bacteria
 Prokaryotic organisms without a cell wall, only having plasma
membrane
 About 200 disease is caused by these organisms
 There are two types:
Spiroplasms - has a distinctive helical morphology
Phytoplasms - oblong, or round, but not spiral
 Phytoplasms not to be grown on artificial media
 In contrast, some Spiroplasma may be grown on artificial media and
transferred to healthy plants
Previously, these organisms considered to be identical with
mykoplasms (also Mollicutes class, rather that attack animals and
humans), however, genetic studies show that they are distant.
 PHYTOPLASMS – previously: Mycoplasma-like organisms spherical or oblong, it is not yet possible to cultivate the media
 Present in the vascular tissue, they are transmitted by insects,
sensitive to antibiotics -tetracyklins, and at a temperature higher than
37 ° C.
EXAMPLES OF DISEASES CAUSED BY PHYTOPLASMAS
Aster yellows
European stone fruit
yellows
Grapevine yellows on
grapevine (Vitis vinifera)
Apple proliferation
on apple (Malus
domestica)
Peach X disease
On peach (Prunus persica)
Pear decline on on pear
(Pyrus communis)
 SPIROPLASMAS - has a distinctive helical morphology
 Transfer by insects
 They may be isolated in pure form from insect vectors and
cultured on artificial medium
EXAMPLES OF DISEASES CAUSED BY SPIROPLASMAS
Corn stunt disease
Citrus stubborn disease
Caused by: Spiroplasma
citri
Caused by:
Spiroplasma kunkelli
SYMPTOMS CAUSED BY MOLLICUTES
EUKARYOTS
Parasitic plants
and Algae
Oomycota
Rhizaria
Plasmodiophorida
Fungi
Insects, mites,
nematodes
SAR
• SAR or Harosa (informally the SAR supergroup) is a clade that
includes STRAMENOPILES (heterokonts), ALVEOLATES, and
RHIZARIA
• The first letter of each group provides the "SAR" in the name
• Members of the SAR supergroup were once included under the
separate supergroups CHROMALVEOLATA and RHIZARIA, until
phylogenetic studies confirmed that stramenopiles and alveolates
diverged together with Rhizaria.
RHIZARIA, group PHYTOMYXEA
PLASMODIOPHOROMYCOTA
Plasmodiophora brassicae,
cause CLUB ROT
• They typically develop within plant
cells, causing the infected tissue to
grow into a gall or scab.
• Important diseases caused by
phytomyxeans include CLUB ROOT in
cabbage and its relatives, and
POWDERY SCAB in potatoes. These
are caused by species of
Plasmodiophora and Spongospora,
respectively.
Beet necrotic yellow vein virus – transfer
by fungus Polymyxa betae
Spongospora subterranea
Cause POWDERY SCAB
LIFE CYCLE - PLASMODIOPHORA BRASSICAE
STRAMENOPILA
• The heterokonts or stramenopiles (formally, Heterokonta or
Stramenopiles) are a major line of eukaryotes currently containing
more than 25,000 known species.
• Most are algae, ranging from the giant multicellular kelp to the
unicellular diatoms, which are a primary component of plankton.
•
Other notable members of the Stramenopiles include the
(generally) parasitic oomycetes, including Phytophthora of Irish
potato famine infamy and Pythium which causes seed rot and
damping off.
• Unicellular or filamentous
organisms, cell wall composed
mostly of cellulose
• Flagella (if present) having at least
one flagellum with rigid
mastigonemata.
DIVISION : OOMYCOTA
• They are filamentous, microscopic,
absorptive organisms that reproduce
both sexually (oogonium and
antheridium – oospore) and asexually
(zoospores in sporangium).
• Oomycetes occupy both saprophytic
and pathogenic lifestyles
SYMPTOMS OF OOMYCOTA INFECTION
OOMYCOTA
Phytophthora infestans Pythium debaryanum
Bremia lactucae
Pseudoperonospora
cubensis
Plasmopara viticola
LIFE CYCLE - PLASMOPARA VITICOLA